Biomechanics of human quadriceps muscles during electrical stimulation

Evaluation of the Combined Application of Neuromuscular Electrical Stimulation and Volitional Contractions on Thigh Muscle Strength, Knee Pain, and Physical Performance in Women at Risk for Knee Osteoarthritis: A Randomized Controlled Trial

BACKGROUND

Knee osteoarthritis (OA) is a leading cause of disability that is associated with quadriceps weakness. However, strengthening in people with or with risk factors for knee OA can be poorly tolerated.

OBJECTIVE

To assess the efficacy of a 12-week low-load exercise program, using a hybrid training system (HTS) that uses the combination of neuromuscular electrical stimulation and volitional contractions, for improving thigh muscle strength, knee pain relief, and physical performance in women with or with risk factors for knee OA.

DESIGN

Randomized, single-blinded, controlled trial.

SETTING

Exercise training laboratory.

PARTICIPANTS

Forty-two women 44-85 years old with risk factors for knee OA.

INTERVENTIONS

Participants randomized to 12 weeks of biweekly low-load resistance training with the HTS or on an isokinetic dynamometer (control).

OUTCOMES

Maximum isokinetic knee extensor torque. Secondary measures included maximum isokinetic knee flexor torque, knee pain (Knee Injury and Osteoarthritis Outcome Score), and timed 20-m walk and chair stand tests.

RESULTS

The HTS and control treatments resulted in muscle strengthening, decreased knee pain, and improved physical performance. HTS group quadriceps and hamstring strength increased by 0.06 ± 0.04 Nm/kg (P > .05) and 0.05 ± 0.02 Nm/kg (P = .02), respectively. Control group quadriceps and hamstring strength increased by 0.03 ± 0.04 Nm/kg (P > .05) and 0.06 ± 0.02 Nm/kg (P = .009), respectively. Knee pain decreased by 11.9 ± 11.5 points (P < .001) for the HTS group and 14.1 ± 15.4 points (P = .001) for the control group. The 20-m walk time decreased by 1.60 ± 2.04 seconds (P = .005) and 0.95 ± 1.2 seconds (P = .004), and chair stand time decreased by 4.8 ± 10.0 seconds (P > .05) and 1.9 ± 4.7 seconds (P > .05) in the HTS and control groups, respectively. These results did not differ statistically between the HTS and control groups.

CONCLUSIONS

These results suggest the HTS is effective for alleviating pain and improving physical performance in women with risk factors for knee OA. However, the HTS does not appear to be superior to low-load resistance training for improving muscle strength, pain relief, or physical function.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02802878.

LEVEL OF EVIDENCE

I.

Electrically Stimulated Antagonist Muscle Contraction Increased Muscle Mass and Bone Mineral Density of One Astronaut - Initial Verification on the International Space Station

BACKGROUND

Musculoskeletal atrophy is one of the major problems of extended periods of exposure to weightlessness such as on the International Space Station (ISS). We developed the Hybrid Training System (HTS) to maintain an astronaut's musculoskeletal system using an electrically stimulated antagonist to resist the volitional contraction of the agonist instead of gravity. The present study assessed the system's orbital operation capability and utility, as well as its preventative effect on an astronaut's musculoskeletal atrophy.

METHODS

HTS was attached to the non-dominant arm of an astronaut staying on the ISS, and his dominant arm without HTS was established as the control (CTR). 10 sets of 10 reciprocal elbow curls were one training session, and 12 total sessions of training (3 times per week for 4 weeks) were performed. Pre and post flight ground based evaluations were performed by Biodex (muscle performance), MRI (muscle volume), and DXA (BMD, lean [muscle] mass, fat mass). Pre and post training inflight evaluations were performed by a hand held dynamometer (muscle force) and a measuring tape (upper arm circumference).

RESULTS

The experiment was completed on schedule, and HTS functioned well without problems. Isokinetic elbow extension torque (Nm) changed -19.4% in HTS, and -21.7% in CTR. Isokinetic elbow flexion torque changed -23.7% in HTS, and there was no change in CTR. Total Work (Joule) of elbow extension changed -8.3% in HTS, and +0.3% in CTR. For elbow flexion it changed -23.3% in HTS and -32.6% in CTR. Average Power (Watts) of elbow extension changed +22.1% in HTS and -8.0% in CTR. For elbow flexion it changed -6.5% in HTS and -4.8% in CTR. Triceps muscle volume according to MRI changed +11.7% and that of biceps was +2.1% using HTS, however -0.1% and -0.4% respectively for CTR. BMD changed +4.6% in the HTS arm and -1.2% for CTR. Lean (muscle) mass of the arm changed only +10.6% in HTS. Fat mass changed -12.6% in HTS and -6.4% in CTR.

CONCLUSIONS

These results showed the orbital operation capability and utility, and the preventive effect of HTS for an astronaut's musculoskeletal atrophy. The initial flight data together with the ground data obtained so far will be utilized in the future planning of human space exploration.

A biomechanical cause of low power production during FES cycling of subjects with SCI

BACKGROUND

The goal of Functional Electrical Stimulation (FES) cycling is to provide the health benefits of exercise to persons with paralysis. To achieve the greatest health advantages, patients should produce the highest possible mechanical power. However, the mechanical power output (PO) produced during FES cycling is very low. Unfavorable biomechanics is one of the important factors reducing PO. The purpose of this study was to investigate the primary joints and muscles responsible for power generation and the role of antagonistic co-contraction in FES cycling.

METHODS

Sixteen subjects with complete spinal cord injury (SCI) pedaled a stationary recumbent FES tricycle at 60 rpm and a workload of 15 W per leg, while pedal forces and crank angle were recorded. The joint muscle moments, power and work were calculated using inverse dynamics equations.

RESULTS

Two characteristic patterns were found; in 12 subjects most work was generated by the knee extensors in the propulsion phase (83% of total work), while in 4 subjects most work was shared between by the knee extensors (42%) and flexors (44%), respectively during propulsive and recovery phases. Hip extensors produced only low net work (12 & 7%). For both patterns, extra concentric work was necessary to overcome considerable eccentric work (-82 & -96%).

CONCLUSIONS

The primary power sources were the knee extensors of the quadriceps and the knee flexors of the hamstrings. The antagonistic activity was generally low in subjects with SCI because of the weakness of the hamstrings (compared to quadriceps) and the superficial and insufficient hamstring mass activation with FES.

Leg general muscle moment and power patterns in able-bodied subjects during recumbent cycle ergometry with ankle immobilization

Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads. Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60 rpm during passive cycling and at two workloads (low 15 W and high 40 W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations. During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0-258°) hip extension moment and a shortened range (350-150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase. For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.

Hybrid-training method increases muscle strength and mass in the forearm without adverse effect of hand function in healthy male subjects

Conventional neuromuscular electrical stimulation (NMES) results in surface muscle contraction but high electrical stimulation intensity is required to activate the deep muscles. Therefore, NMES is not useful for training at complicated sites such as the forearm. To make NMES more effective we developed a hybrid training method (HYB), consisting of electrically stimulated antagonists to resist agonist muscle contractions. The purpose of this study was to compare the effects of HYB on the forearm as compared with NMES alone, and to determine whether HYB had any adverse effects on complex hand movements. Thirty subjects were randomly distributed into three groups: a HYB program group, an isometric electrical stimulation group (ES), and a control group (CN). Subjects trained 3 times a week for 6 weeks. Each session consisted of 10 sets of 10 reciprocal 2-sec wrist flexions and extensions separated by 1-min rest intervals. Wrist flexion/extension torques, grip strengths (GS), forearm flexor/extensor cross sectional areas (CSA), and hand dexterity (Purdue Pegboard (PEG) test, finger tapping (Tapping) test were measured. The HYB group demonstrated statistically significant increases in wrist extension torques (22.8%, p<0.01), forearm flexor CSA (9.6%, p<0.01), and in forearm extensor CSA (5.1%, p<0.05) at the end of training. There was no increase in torque or CSA in the ES or CN groups. Hand dexterity showed no significant differences in any of the three groups. HYB had no adverse effect on hand function and was more effective in forearm training than NMES alone.

Increasing muscle strength and mass of thigh in elderly people with the hybrid-training method of electrical stimulation and volitional contraction

The "Hybrid training" (HYBT) method utilizing combined electrical stimulation and voluntary muscle contraction has been developed as a muscle training method. It has already been shown that the method is technically sound and clinically effective in healthy young subjects. The purpose of this study was to investigate the effect of the HYBT method on the knee extensor strength considering safety for elderly people. Twenty subjects were randomly divided into two groups: the HYBT group and the weight machine training (WMT) group. All the subjects performed knee flexion and extension for 19 min per session, twice a week for 12 weeks. At the baseline and after the training, the subjects' maximal isometric torque of knee extension and cross-sectional area (CSA) of quadriceps femoris muscle were measured. The subjects completed the study without adverse effects. The knee extension torque significantly increased in both groups (39% in HYBT group and 42% in WMT group, P < 0.05). The CSA of quadriceps whole significantly increased in both groups (9% in HYBT group and 14% in WMT group, P < 0.05). These results indicate that the HYBT method increases muscle strength and mass, and that this method is as effective as the WMT. In addition, unlike the WMT, the HYBT device, which is portable and not large in size, is so easy to handle that it can be placed at the bedside. Therefore, the HYBT has potential to become a safe, effective method of muscle training for elderly people.

Development of a mathematical model for predicting electrically elicited quadriceps femoris muscle forces during isovelocity knee joint motion

Background

Direct electrical activation of skeletal muscles of patients with upper motor neuron lesions can restore functional movements, such as standing or walking. Because responses to electrical stimulation are highly nonlinear and time varying, accurate control of muscles to produce functional movements is very difficult. Accurate and predictive mathematical models can facilitate the design of stimulation patterns and control strategies that will produce the desired force and motion. In the present study, we build upon our previous isometric model to capture the effects of constant angular velocity on the forces produced during electrically elicited concentric contractions of healthy human quadriceps femoris muscle. Modelling the isovelocity condition is important because it will enable us to understand how our model behaves under the relatively simple condition of constant velocity and will enable us to better understand the interactions of muscle length, limb velocity, and stimulation pattern on the force produced by the muscle.

Methods

An additional term was introduced into our previous isometric model to predict the force responses during constant velocity limb motion. Ten healthy subjects were recruited for the study. Using a KinCom dynamometer, isometric and isovelocity force data were collected from the human quadriceps femoris muscle in response to a wide range of stimulation frequencies and patterns. % error, linear regression trend lines, and paired t-tests were used to test how well the model predicted the experimental forces. In addition, sensitivity analysis was performed using Fourier Amplitude Sensitivity Test to obtain a measure of the sensitivity of our model's output to changes in model parameters.

Results

Percentage RMS errors between modelled and experimental forces determined for each subject at each stimulation pattern and velocity showed that the errors were in general less than 20%. The coefficients of determination between the measured and predicted forces show that the model accounted for ~86% and ~85% of the variances in the measured force-time integrals and peak forces, respectively.

Conclusion

The range of predictive abilities of the isovelocity model in response to changes in muscle length, velocity, and stimulation frequency for each individual make it ideal for dynamic applications like FES cycling.

Inevitable joint angular rotation affects muscle architecture during isometric contraction

The purpose of this study was to quantify the influence of inevitable ankle joint motion during an isometric contraction on the measured change of the gastrocnemius medialis muscle (GM) architecture in vivo during the loading and the unloading phase. Sitting on a dynamometer subjects performed isometric maximal voluntary contractions as well as contractions induced by electrostimulation. Synchronous joint angular motion, plantarflexion moment, foot's centre of pressure and real-time ultrasonography of muscle architecture changes of the GM were obtained. During the contraction the ankle joint position altered and significantly affected the change in muscle architecture. At maximal tendon force (1094+/-323 N), the measured fascicle length overestimated the change in fascicle length due to the tendon force by 1.53 cm, while the measured pennation angle overestimated the change in pennation angle due to the tendon force by 5.5 degrees . At the same tendon force the measured fascicle length and pennation angle were significantly different between loading and unloading conditions. After correcting the values for the change in ankle joint angle no differences between the loading and the unloading phase at the same tendon force were found. Concerning the estimation of GM fascicle length-force and pennation angle-force curves during the loading and unloading phase of an isometric contraction, these findings indicate that not accounting for ankle joint motion will produce unreliable results.

Dynamic simulation of FES-cycling: influence of individual parameters

Cycling by means of functional electrical simulation (FES) is an attractive training method for spinal cord injured (SCI) subjects. FES-cycling performance is influenced by a number of parameters like seating position, physiological parameters, conditions of surface stimulation, and pedaling rate. The objective of this paper was the determination of the influence of the most important parameters on optimal muscle stimulation patterns and power output of FES-cycling on a noncircular pedal path. The rider-cycle system was modeled as a planar articulated rigid body linkage on which the muscle forces are applied via joint moments and implemented into a forward dynamic simulation of FES-cycling. For model validation, the generated drive torques that are predicted by the simulation were compared to measurements with an individual paraplegic subject. Then, a sensitivity analysis was carried out to determine the influences of the most important parameters for surface stimulation of gluteus maximus, quadriceps, hamstrings, and peroneus reflex. The results show how optimal stimulation patterns and the expected mean active power output can be estimated based on measured individual parameters and adjusted geometry and stimulation parameters for a particular SCI-subject. This can considerably improve FES-cycling performance and relieve the patients by shortening the time that is necessary for experimental adaptation of the stimulation patterns.

Quantitative analysis of ankle hypertonia after prolonged stretch in subjects with stroke

The aims of this study are to validate the hypertonia treatment/assessment system and to quantify the immediate effect of prolonged muscle stretch (PMS) on the inhibition of ankle hypertonia in stroke patients. For PMS treatment, ankle plantarflexors were stretched with a constant torque in 25 subjects with hemiplegia and ankle plantarflexors hypertonia. Using the developed hypertonia treatment/assessment system, the effects of the PMS treatment were quantified by comparing the reactive torque measurements of the ankle joint before and after the treatment sessions in terms of elastic (elastic-inertia) (K(ei)) and viscous (K(v)) components. It was shown that an application of PMS for 30 min using a constant stretching force, approximately 80% of the torque measured at the maximal passive ROM dorsiflexion position, significantly reduces both components of the ankle joint torque (P < 0.05). The present results suggested that the application of PMS with a constant torque could reduce not only the elasticity of the hypertonic muscles, but also their viscosity in the stroke patients.

Agonist contractions against electrically stimulated antagonists

OBJECTIVE

To assess an exercise program that uses electrically stimulated antagonists to resist agonist muscle contractions.

DESIGN

In 1 limb, electrically stimulated antagonists resisted elbow flexion and extension. In the other, stimulation occurred without volitional muscle contraction.

SETTING

A biomechanics laboratory in Japan.

PARTICIPANTS

Twelve men between the ages of 19 and 24 years. Subjects served as their own controls.

INTERVENTION

Subjects trained 3 times a week for 12 weeks. Each session consisted of 10 sets of 10 elbow flexor and extensor contractions.

MAIN OUTCOME MEASURES

Isokinetic elbow extension and flexion torques. Biceps and triceps brachii cross-sectional areas.

RESULTS

Elbow extension torques increased (32.85% at 30 degrees/s, 27.20% at 60 degrees/s, 26.16% at 90 degrees/s; all P<or=.02) over the training period in limbs that trained against electrically stimulated antagonists. Control limb extension torque increases were smaller (8.52% -14.91%) and did not reach statistical significance. Elbow flexion torques improved in both groups, but the changes did not reach statistical significance. Cross-sectional areas increased in all muscles but were most marked in the antagonist stimulated limbs: triceps 16.20% versus 4.25% (P=.01) and biceps 16.65% versus 7.00% (P=.005).

CONCLUSIONS

Exercises that use electrically stimulated antagonist muscles may be effective in increasing muscle strength and mass.

MRI quantification of muscle activity after volitional exercise and neuromuscular electrical stimulation

OBJECTIVE

The efficacy, and even the depth, of muscle stimulation during surface electrode neuromuscular electrical stimulation (NMES) is a matter of debate. This study addresses these issues by assessing the utility of a magnetic resonance imaging (MRI) technique in localizing and quantitating changes in the nature of MRI signals in the quadriceps muscle after volitional exercise and NMES.

DESIGN

Volitional isometric and NMES-evoked quadriceps muscle activity was evaluated in two controlled trials. In the first, isometric quadriceps strength was determined during NMES and maximal volitional isometric exercise in six healthy men. In the second, changes in the ratio of MRI T2 signal intensities before and after volitional isometric exercise and NMES were used to quantitate MRI signal changes associated with muscle activation in 12 additional healthy men.

RESULTS

MRI clearly detected quadriceps muscle tissue activation after both volitional and stimulated contractions, even though the NMES knee extension torque was only 23.5% that of maximal volitional isometric exercise. In particular, the T2 intensity ratios increased 26.5% +/- 17.3% (mean +/- standard deviation) after volitional exercise and 12.9% +/- 12.8% after NMES. This pattern of volitional isometric exercise, producing larger T2 intensity ratio values than NMES, was present in both deep and superficial layers and throughout the quadriceps muscle.

CONCLUSIONS

Although volitional muscle contractions were several times stronger than those induced by NMES in this study, our findings support the idea that MRI can provide a noninvasive way to quantitate and localize volitional and electrically stimulated muscle activation.

Interaction of array of finite electrodes with layered biological tissue: effect of electrode size and configuration

A hybrid scheme, combining image series and moment method has been utilized for the calculation of the intramuscular three-dimensional (3-D) current density (CD) distribution and potential field transcutaneously excited by an electrode array. The model permits one to study the effect of tissue electrical properties and electrode placement on the CD distribution. The isometric recruitment curve (IRC) of the muscle was used for parameter estimation and model verification, by comparison with experimentally obtained IRCs of functional electrical stimulation (FES)-activated quadriceps muscle of paraplegic subjects. Sensitivity of the calculated IRC to parameters such as tissue conductivity, electrode size, and configuration was verified. The resulting model demonstrated characteristic features that were similar to those of experimentally obtained data. The model IRCs were insensitive to the electrode size; however, the inclusion of the bone-fascia layer significantly increased the intramuscular CD and, consequently, increased the IRC slope. Of the different configurations studied, a four-electrode array proved advantageous because, in this case, the CD between the electrodes was more evenly distributed, providing better resistance to fatigue. However, due to the steeper linear portion of the IRC, this configuration suffered from a somewhat reduced controllability of the muscle.

Test bed with force-measuring crank for static and dynamic investigations on cycling by means of functional electrical stimulation

Cycling by means of functional electrical stimulation (FES) is an attractive training method for individuals with paraplegia. The physiological benefits of FES are combined with the psychological incentive of independent locomotion. In addition, cycling has the advantage in that the generated muscle forces are converted into drive power with relatively high efficiency compared to other means of locomotion, e.g., walking. For the design of an appropriate cycling device and the development of optimal stimulation patterns, it has to be investigated how the geometry for FES cycling, influenced by individual parameters of the FES-generated drive torques and the magnitude of variations among subjects with paraplegia, can be optimized. This study shows the design of a freely adjustable test bed with additional motor drive which allows static and dynamic measurements of force components and drive torque at the crank. Furthermore, the influence of geometry and various individual parameters on FES pedaling can be tested for each subject individually. A pedal path realized by a three-bar linkage that was optimized according to preliminary simulations further increases leg cycling efficiency. Safety precautions avoid injuries in case of excessive forces, e.g., spasms. Test results illustrate the application of the test bed and measurement routines. A test series with four paraplegic test persons showed that the presented static and dynamic measurement routines allow to provide optimal stimulation patterns for individual paraplegic subjects. While pedaling with these optimal stimulation patterns only negligible negative active drive torques, due to active muscle forces, were applied to the crank and sufficient drive power was generated to power a cycle independently.

Isometric muscle length-tension curves do not predict angle-torque curves of human wrist in continuous active movements

In this study we tested the hypothesis that during steady contractions of human wrist extensors or flexors, the torque-angle relationship during movements imposed about the wrist is predicted by the classical isometric muscle length-tension curve, with ascending, descending and ascending limbs. Angle-torque relationships were measured during steady muscle activation (10% of maximal voluntary contraction: MVC), elicited either by electrical stimulation or voluntary regulation of the electromyogram (EMG). Flexion-extension movements of constant speed (+/-10 degrees /s) were imposed on the subjects' hands with a servo actuator, either through the full physiological range of motion +/-50 degrees, or through +/-10 degrees. During extensor contractions, angle-torque curves in +/-50 degrees movements had ascending, descending and ascending limbs, as in isometric contractions. However, in +/-10 degrees movements, torque always increased with increasing muscle length and decreased with decreasing length, even over angles corresponding to the descending limb of isometric curves. For flexor activation, angle-torque curves had similar properties, though descending limbs were less obvious or absent. During imposed movements, hysteresis was observed in the angle-torque curves. This was attributed to non-linearities of the active muscles. Hysteresis reached a maximum at intermediate wrist angles and declined at maximal muscle length, contradicting the recent hypothesis that sarcomere non-uniformity is responsible for the hysteresis. We conclude that the classical isometric length-tension curve, with its prominent descending limb, does not predict angle-torque curves of human wrist muscles in continuous movements. A more appropriate model is one in which stiffness about the wrist is always positive and hysteresis is a significant factor.